In a mobile communication system, a telecommunication carrier, which provides services in advance, sets a cell coverage, that is, a service area corresponding to a mobile terminal in each radio base station (hereinafter referred to as “base station”). The telecommunication carrier sets a radio parameter of a tilt angle of an antenna or the like to the base station to obtain the service area. When the telecommunication carrier sets a prescribed radio parameter and starts an operation of the system, the service area that is scheduled in advance may not be obtained because of a change of an operation condition of the system or of a radio environment (for example, a change of a path loss due to a new building).
To maintain the quality of the communication service provided to a user of the system, the telecommunication carrier measures the service area of the base station by measuring a reception power in a mobile terminal of the radio signal from the base station by a wave measuring device or the like. The service area as the measurement result is compared with the service area that is scheduled to be a target in advance, and the change of the radio parameter is performed regularly or irregularly if desired. The above-described change of the radio parameter is performed according to the change of the radio environment such as a traffic change or the like, so that a high cost for security is desired. According to the mobile communication system, there is a known tilt angle determining method for dynamically adjusting the tilt angle of the antenna of the base station (International Publication Pamphlet No. WO2005/013632 or the like). The known tilt angle determining method includes an operation for setting an initial value of the tilt angle, an operation for calculating a deterioration rate of the system (the service area or the like) in which the tilt angle has the initial value, an operation for selecting an antenna that decreases the tilt angle, an operation for decreasing the tilt angle of the selected antenna, an operation for calculating the deterioration rate obtained when the tilt angle is decreased, and an operation for repeating continuation determination of the processing for decreasing or increasing the sequence of tilt angles. The known tilt angle determining method further includes an operation for outputting the tilt angle of which the deterioration rate is decreased and an operation for determining the end of the repeating processing of the above-described operations.
According to the above-described conventional method for dynamically adjusting the tilt angle of the antenna, a device that determines the tilt angles of the antennas of a plurality of base stations is provided. The device observes the quality change inside the area to retrieve an optimum tilt angle while changing the tilt angle of each of the base stations to retrieve the optimum tilt angle. That is, the processing for calculating the deterioration rate of the system every time the tilt angle is slightly changed and for repeating the change of the tilt angle until the deterioration rate is acceptable. As a result, retrieving the optimum value of the tilt angle takes time, so that the reception quality inside the area may frequently change during the retrieval of the optimum value.